1. Field of the Invention
The present invention relates to the configuration of a contact portion of a semiconductor device typified by a thin-film transistor as well as to a method of forming it.
2. Description of the Related Art
FIGS. 2A to 2E schematically show a conventional, old process used in a thin-film transistor manufacturing process, for instance. Specifically, this process is to take contact to a semiconductor layer formed on a glass substrate or a quartz substrate.
First, as shown in FIG. 2A, a semiconductor layer 202 is formed on a substrate 201 having an insulative surface. The substrate 201 is a quartz or glass substrate. The semiconductor layer 202 is an amorphous or crystalline silicon film. For example, the semiconductor layer 202 shown in FIG. 2A is part of an active layer of a thin-film transistor.
Next, an insulating film 203 is so formed as to cover the semiconductor layer 202. The insulating film 203, called an interlayer insulating film, is a silicon oxide film or a silicon nitride film. (FIG. 2B)
Then, an opening 204 called a contact hole is formed through the insulating film 203. (FIG. 2C)
Finally, a wiring line 205 is formed with such a material a metal or a silicide, to complete a contact portion (FIG. 2D)
However, as the semiconductor layer 202 pattern is miniaturized and is made finer, there may occur an erroneous positional relationship between the contact hole 204 and the semiconductor layer 202 as shown in FIG. 2E. This may result in etching of the substrate 201. Where a silicon oxide film as an undercoat film is formed on the substrate 201, it may be etched in a similar manner. This may later cause a contact failure, a line disconnection, and other failures.
The above erroneous positional relationship can be caused by a mask registration error in forming the contact hole 204, a mask registration error in forming the semiconductor layer 202 pattern, and other factors. In many cases, these factors occur in combination.
The state of FIG. 2E may be a cause of a failure in a manufacturing process. Although this problem can be solved by increasing the patterning accuracy and the accuracy of contact hole formation, these measures can cause other undesired effects such as an increase in manufacturing cost and reduction in productivity.